Is it a cold or an allergic reaction? For most people, a runny nose in winter is usually a sign of an ordinary cold. Who would think about pollen in December? But one type of tree does plague allergy sufferers even this early in the season. The culprit is called the Spaeth’s alder (Alnus spaethii).

In a cross-sectional study conducted in 1986 and 2006, a team of Swiss researchers examined the allergy symptoms of 15-year-old students from Grabs (Switzerland). They noticed that the subjects in the later study reacted more frequently to alder pollen than the subjects in the 1980s. Based on pollen count measurements, the researchers discovered that the pollen load in the region had increased due to alder pollen and also began earlier. They soon found out why: 96 Spaeth’s alders had been planted in the city of Buchs near Grabs at the beginning of the 2000s.

The Spaeth’s alder is a cross between the Japanese and the Caucasian alder. It was bred at the beginning of the 20th century and enjoyed great popularity in cities for its beautiful leaves and rapid growth. It is also especially weather resistant compared to the native alder. Scientists suspect that this is why it begins to bloom as early as the end of December – around two months before the native alder. Climate change and urban lighting may be other triggers.

When planting new trees, cities and municipalities would do allergy sufferers a service by avoiding the Spaeth’s alder.